Dual stage actuator suspension having a single microactuator and employing pseudo symmetry to achieve suspension balance

ABSTRACT

A dual stage actuator (DSA) suspension has a single microactuator such as a PZT element on one side of central longitudinal axis of the suspension, and a pseudo symmetry structure formed or affixed on the other side of the central longitudinal axis opposite the PZT. The pseudo symmetry structure has mass and stiffness that mirrors the PZT, thus keeping the suspension mechanically balanced and symmetric about the longitudinal axis for improved suspension performance especially in a shock environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 61/152,865 filed Feb. 16, 2009, the disclosure ofwhich is incorporated by reference herein as if set forth in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of hard disk drive suspensionshaving dual stage actuators. More particularly, this invention relatesto the field of a dual stage actuator suspension for a hard disk drive,the suspension having a single microactuator device and employing pseudosymmetry to balance the suspension.

2. Description of Related Art

In a hard disk drive, the suspension is the component that holds theread-write head over the desired data track on the spinning magnetichard drive. The disk drive could also be an optical disk or possiblyother data storage technologies. As track densities increase and drivesare made smaller, there is a constant need in the industry for greaterprecision in the disk drive components including the actuator(s) thatmove the read-write head to the correct data track.

Suspensions have been proposed that have dual stage actuators (DSAs),with the first stage being the voice coil motor that traditionally hasmoved the suspension, and the second stage being a microactuator mountedon the suspension itself that makes extremely fine adjustments to thehead position. The microactuator typically comprises a pair ofpiezoelectric devices such as lead zirconate titanate (PZT) devicesmounted in a push-pull configuration, such that one PZT pulls one sideof the suspension while the other PZT pushes the other side. Forpurposes of the present disclosure and for purposes of simplicity ofdiscussion, the microactuator will generally be referred to as a PZTalthough it will be understood that microactuators other than PZTs canbe used. Representative of a dual PZT type DSA suspension are U.S. Pat.No. 6,614,627 issued to Shimizu et al, and U.S. Pat. No. 6,731,472issued to Okamoto et al, which describe DSA suspensions using PZTdevices as the microactuators. Those patents employ two non-split PZTs.A non-split PZT, also called a single pole PZT, is a PZT which has onlya single electrical pole per face. FIG. 1 is a representativeillustration of a DSA type suspension having two single-pole PZT's 8 and9 according to the prior art.

Another known design uses a split PZT. A split PZT is a single device inwhich the device is split into two portions that can be drivenseparately, such that a single device is capable of both expanding onone side and contracting on the other side. Split PZT's are typicallyformed by metalizing both the top face and the bottom face of thedevice, with a split line in the middle created by photo patterning. Asplit PZT behaves as if it is two separate PZTs. Split PZTs typicallyhave three electrical connections: a right side driving voltageconnection, a left side driving voltage connection, and a common groundconnection.

Other configurations of PZT microactuated suspensions have beenproposed. U.S. Pat. No. 6,381,104 issued to Soeno et al. shows apiezoelectric moving-slider microactuator that moves the slider byrotation. U.S. Pat. No. 7,382,583 issued to Hirano et al. describes aDSA suspension that uses a rotary piezoelectric microactuator.

DSA suspensions that use a microactuator other than a PZT microactuatorhave also been proposed. U.S. Pat. Nos. 5,959,808 issued to Fan et al.and 5,995,334 issued to Fan et al. describe electrostatic microactuatorsfor suspensions.

DSA suspensions have also been proposed using PZTs in various locations,including on the mount plate, on the load beam, or on the gimbal tongueclose to the slider.

Due to the additional cost of DSA suspensions over traditionalsuspensions, it is believed that DSA suspensions have only been recentlybecome available commercially. There is therefore a need for reducingmanufacturing costs of DSA suspensions.

SUMMARY OF THE INVENTION

The present invention is of a DSA type suspension requiring only asingle non-split PZT microactuator, but which nevertheless is balancedabout the central longitudinal axis of the suspension or load beam towithin an acceptably high degree of mass balance and inertial balance. Amechanically balanced suspension will generally perform better, such asby not twisting in response to vertical movements of the suspension asthe disk surface flutters or as the drive is bumped.

To achieve the balancing, an element which will be called herein apseudo symmetry structure or element, or balancing structure or element,is either mounted to or fabricated on the suspension in a locationgenerally opposite the microactuator. The pseudo symmetry element isdesigned such that it has a mass, a stiffness, and preferably a massdistribution that generally correspond to the microactuator, thus makingthe suspension generally symmetric about the longitudinal axis asmeasured by mass, stiffness, inertial distribution, and other relevantparameters.

A DSA suspension according to the present invention therefore typicallyhas a central longitudinal axis, a PZT microactuator mounted on a firstside of the central longitudinal axis for making fine radial adjustmentsin the position of a read-write head at or near the distal end of thesuspension, and a pseudo symmetry structure on a second and oppositeside of the central longitudinal axis, the pseudo symmetry structuremimicking the mechanical properties of the PZT and being generallydisposed in mirror relation thereto. The pseudo symmetric structure iscreated such that it has similar mass and stiffness, and preferablysimilar mass distribution, as that of the PZT, in order to keep thesuspension inertially symmetric about the central longitudinal axis.

In a first embodiment, the pseudo symmetry structure comprises astainless steel pseudo symmetry element that is welded or otherwiseaffixed to the suspension on a first side of a central longitudinal axisof the suspension generally opposite the PZT mounted on the second sideof the central longitudinal axis. The pseudo symmetry element isgenerally symmetrical about both its x and y horizontal axes, and has acentral hole therethrough in order to give the pseudo symmetry structurea spring-like stiffness that generally matches the spring-like stiffnessof the PZT.

By requiring only a single non-split PZT instead of either two non-splitPZTs or a single split PZT as in previous designs, the present inventionallows for simpler and therefore lower cost DSA suspensions thatnevertheless are acceptably symmetrical about the longitudinal axis.This is true regardless of whether the microactuator is located on themount plate, on the beam portion, on the gimbal tongue, or anywhere elseon the suspension.

Exemplary embodiments of the invention will be further described belowwith reference to the drawings, in which like numbers refer to likeparts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a prior art DSA suspension employing twonon-split PZTs.

FIG. 2 is a top plan view of a DSA suspension according to a firstembodiment of the present invention.

FIG. 3 is a top plan view of pseudo symmetry element 12 of thesuspension of FIG. 2.

FIG. 4A is a top plan view of a DSA suspension having a single non-splitPZT and a pseudo symmetry structure according to a second embodiment ofthe invention.

FIG. 4B is a bottom plan view of the suspension of FIG. 4A.

FIG. 5 is a top plan view of the pseudo symmetry component of thesuspension of FIG. 4A.

FIG. 6 is a top plan view of a suspension having a spring feature formedintegrally in the suspension in order to balance the stiffnesscharacteristics of the PZT microactuator, according to a furtherembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a top plan view of a DSA suspension 100 having PZT 10 andbalancing structure or pseudo symmetry structure 12 according to a firstembodiment of the present invention. PZT 10 has convention electricalconnections thereto (not shown) that will add somewhat to the weight andinertial characteristics of PZT 10. For purposes of the presentdiscussion throughout this disclosure and the appended claims, what willbe referred to as the PZT or other microactuator encompasses theelectrical connections thereto and their weights. Pseudo symmetrystructure 12 may be fabricated separately and thereafter affixed tosuspension 100 such as by an adhesive such as epoxy, or by laserwelding. It is currently anticipated that the preferred embodiment willinclude at least one added stainless steel component that is formedseparately and later affixed to the suspension by welding. Accordingly,in the discussion that follows, although the pseudo symmetry structurecomponent will be referred to for brevity as being welded to thesuspension, it will be understood that the component could be affixed tosuspension 100 by any other suitable means. PZT 10 and pseudo symmetrystructure 12 are located on opposite sides of central longitudinal axis30 of suspension 100, in generally mirror relation. That is, PZT 10 andpseudo symmetry structure 12 lie on opposite lateral sides of suspension100. In the embodiment, suspension 100 has two gaps 50 and 52 formedtherein, with the voids being generally of the same size and shape anddisposed in mirror relation about central longitudinal axis 30. PZT 10spans first void 50, and pseudo symmetry structure 12 spans second gap52, also in generally mirror relation about central longitudinal axis30, with pseudo symmetry structure 12 welded across gap 52.

Alternatively, instead of being welded to suspension 100, pseudosymmetry structure 12 may be integrally formed with suspension 100 byetching, stamping, laser cutting, or otherwise working suspension 100,or by a combination of working the suspension and adding material.Pseudo symmetry structure 12 can be either thicker, thinner, or the samethickness as, the surrounding stainless steel, due to the ability toselectively etch away stainless steel material from either the area ofthe stainless steel sheet that will become pseudo symmetry structure 12and/or from the area that will become the mount plate, the load beam, orother structure with which pseudo symmetry structure 12 will beintegrally formed.

PZT 10 and pseudo symmetry structure 12 can be located on a tip of mountplate 14, also referred to as the base plate, near and proximal tosuspension springs 16 as shown in FIG. 2, or could be located on beamportion 18 of load beam 20, or on gimbal tongue 22, or in any othersuitable location as will be apparent to those skilled in the relevantart.

Pseudo symmetry structure 12 preferably matches the PZT 10 to within40%, and more preferably to within 20%, and more preferably still towithin 10%, and more preferably still to within 5%, in each of theparameters of mass, stiffness, inertial distribution, and any otherrelevant parameters, with the result that the overall suspension is massand inertially balanced about the central longitudinal axis to within atleast 10%, and preferably to within 5%, and more preferably still towithin 2%.

FIG. 3 is a top plan view of pseudo symmetry structure 12 of suspension100 of FIG. 2. Pseudo symmetry structure 12 has a central hole 13 and issymmetric about two horizontal axes 32 and 34. If pseudo symmetrystructure 12 is formed integrally with the stainless steel suspension100 by etching, stamping, or other forming operation that is otherwisepart of the load beam manufacturing process, then no additional partswill be required to be formed and affixed to the suspension 100,resulting in substantial manufacturing cost reduction. Alternatively,pseudo symmetry structure 12 could be formed separately of differentmaterials or combinations of materials and thereafter affixed tosuspension 100 such as by laser welding, adhesive, or by other knownmethods. Regardless of whether pseudo symmetry structure 12 isintegrally formed with suspension 100 or is separately formed andthereafter affixed thereto, pseudo symmetry structure 12 will notrequire an electrical circuit trace to be routed thereto andelectrically connected thereto, thus eliminating the cost associatedwith routing and connecting electrical circuits to a second PZT, or tothe second half of a split PZT, as in prior art designs. Even if PZT 10is a split PZT, simplicity and cost savings are still realized becausethe electrical traces needed to drive the two halves of the PZT arerouted and connected to only one side of suspension 10 while stillmaintaining pseudo symmetry and balance of suspension 100.

FIG. 4A is a top plan view of a DSA suspension 200 having a singlenon-split PZT 210 and a pseudo symmetry structure 212 according to asecond embodiment of the invention. This embodiment is similar to theembodiment of FIG. 2 except that the shape of pseudo symmetry structure212 is different.

FIG. 4B is a bottom plan view of the suspension of FIG. 4A. This viewshows magnetic head slider 260 which is a conventional head slider. Inoperation, PZT microactuator 210 expands or contracts in response to amicroactuator driving voltage applied thereto causing the distal end ofsuspension 200 carrying head slider 260 to move slightly up or down asoriented in the figure, thus effecting microfine movements of headslider 260 in order to keep head slider 260 properly positioned over thedesired data track on the magnetic disk surface (not shown). Pseudosymmetry element 212 counterbalances PZT both statically and inertially.

FIG. 5 is a top plan view of the pseudo symmetry structure 212 of thesuspension of FIG. 4A.

In the embodiments of FIGS. 2-5 and with particular reference to FIG. 5,the balancing structures have a generally ring shape having a centralhole 213 or other aperture formed therein. By adjusting the size andshape of central hole 213, the ring inner and outer diameters, the shapeand contours of the ring, the thickness of the ring, and the stiffnessof the pseudo symmetry structure 212 in the x, y, and z directions, thepseudo symmetry structure 212 can be made to have mechanical propertiesthat generally mirror the corresponding mechanical properties of PZT210.

Pseudo symmetry structure 212 need not have a single central hole 213therethrough, but could instead have a plurality of holes, slots, orother apertures formed therein, or adjacent portions of the suspension100 could have one or a plurality of holes, slots, or apertures formedtherein, so long as the overall balancing structure generally mirrorsthe characteristics of PZT 210. The pseudo symmetry structure 212 neednot be flat, but could in general have any three dimensional shape. Athree dimensional shape, similar to the shape of PZT 210 itself, couldbetter simulate and thus mirror the inertial components of PZT 210 inthe three linear directions and the three rotational directions.

The characteristics of pseudo symmetry structure 212 can be furthermodified, either over its entirety or locally, by other processingtechniques as well. A first such possible technique is partial etchingof pseudo symmetry structure 212 on either side or both sides to createdepressions, mesas, ridges, valleys, or any other contoured features,similar to the triangular partial etch patterns visible in FIG. 6 insuspension 300 in its load beam near the suspension springs. Thematerial of pseudo symmetry structure 212 could also be modified bylocalized laser irradiation. Still further, the material could bemodified by heat treating, although heat treating is currentlyconsidered undesirable because the stainless steel foil used to make thesuspensions is usually strain hardened, and heat treating wouldtherefore undesirably anneal the steel. Other techniques to modify thecharacteristics of pseudo symmetry structure, either overall or locally,will be apparent to those skilled in the art of materials science andmaterials processing. All of those techniques can allow focusedtailoring of stiffness and deflection in pseudo symmetry structure 212in the x, y, and z axes. Laser irradiation and various other localizedmaterial processing techniques could also be used to locally tailor thecharacteristics of the stainless steel elsewhere on the suspension toassist in the overall balancing of the suspension.

Although PZT 210 will in most cases be the component of suspension 200that contributes the most to non-symmetry of suspension 200, othercomponents including but not limited to the electrical signal trace (notshown) could contribute to static and inertial asymmetry of suspension200. Pseudo symmetry structure 212 could be designed to at leastpartially compensate for those other asymmetries as well therebycounterbalancing those other asymmetries.

Additionally, the balancing structure need not be a single pseudosymmetry element that by itself counterbalances PZT 210. Rather, theoverall pseudo symmetry structure could be comprised of a tab, spring,and/or other structure(s) integrally formed with one or more componentsof suspension 100, combined with a spring element, weight, or otherelement, preferably of stainless steel welded to the suspension, suchthat the combined characteristics of the component(s) of the pseudosymmetry structure that are formed integrally with suspension 100combined with the component(s) of the pseudo symmetry structure that areformed separately and later affixed to suspension 100 generally mirrorand therefore counterbalance the characteristics of PZT 210 located onthe other side of the central longitudinal axis of suspension 200. Sucha more generally pseudo symmetry structure or balancing structure isshown in FIG. 6 which is described below.

FIG. 6 is a top plan view of a suspension having a spring feature formedintegrally in the suspension in order to balance the stiffnesscharacteristics of the PZT microactuator, according to a furtherembodiment. In particular, suspension 300 has a pseudo symmetrystructure 312 comprising several different components, specifically:aperture 342 formed in suspension 300; a spring 340 formed integrallywith suspension 300; a portion 344 of the suspension which is not etchedaway and which therefore does not mirror the cavity across which PZT 310extends, and an added weight 346 welded to suspension 300. Takentogether, suspension portion 344, aperture 342, spring 340, and addedweight 346 define pseudo symmetry structure 312 which counterbalancesPZT 310. Preferably unremoved suspension portion 344, aperture 342,spring 340, and added weight 346 are all adjacent each other, andpreferably all of those elements lie within a common area that is lessthan or equal to the size of the area occupied by PZT 310.

In all of the embodiments shown, the pseudo symmetry structures 12 and212, and spring 340, are designed with the knowledge of how thestiffness of the PZT compares to the stiffness of the stainless steelused for the pseudo symmetry structures. For the embodiment shown inFIG. 6, typically, the stiffness of the PZT 310 will be about one thirdthe stiffness of the stainless steel in spring 340, where the stainlesssteel in spring 340 has the same thickness as the thickness of the tipof the mount plate to which the suspension springs are attached.

The present invention can be used in combination with microactuatorsother than PZTs. Additionally, the present invention can be applied tosuspensions regardless of where the microactuator is located on thesuspension, including suspensions in which the microactuator is locatedon the mount plate, on the load beam, on the gimbal tongue, or any otherlocation.

Although the present invention enables a DSA suspension to beconstructed using a single, single-pole PZT, the invention is applicableand can be used in other contexts as well. For example, the inventioncould be employed with a single split-pole PZT, or even with multiplePZTs in a hard drive suspension or other product where it would bedesirable to mimic a PZT microactuator or other component.

It will be understood that the terms “approximately,” “about,”“substantially,” and “generally” as used within the specification andthe claims herein allows for a certain amount of variation from anyexact dimensions, measurements, arrangements, and characteristics, andthat those terms should be understood within the context of thedescription and operation of the invention as disclosed herein.

It will further be understood that terms such as “top,” “bottom,”“above,” “below,” “horizontal,” and “vertical” as used within thespecification and the claims herein are terms of convenience that denotethe spatial relationships of parts relative to each other rather than toany specific spatial or gravitational orientation. Thus, the terms areintended to encompass an assembly of component parts regardless ofwhether the assembly is oriented in the particular orientation shown inthe drawings and described in the specification, upside down from thatorientation, or any other rotational variation.

It will be appreciated that the term “present invention” as used hereinshould not be construed to mean that only a single invention having asingle essential element or group of elements is presented. Similarly,it will also be appreciated that the term “present invention”encompasses a number of separate innovations which can each beconsidered separate inventions. Although the present invention has thusbeen described in detail with regard to the preferred embodiments anddrawings thereof, it should be apparent to those skilled in the art thatvarious adaptations and modifications of the present invention may beaccomplished without departing from the spirit and the scope of theinvention. Accordingly, it is to be understood that the detaileddescription and the accompanying drawings as set forth hereinabove arenot intended to limit the breadth of the present invention, which shouldbe inferred only from the following claims and their appropriatelyconstrued legal equivalents.

1. A suspension for a hard disk drive having: a microactuator on a first side of a central longitudinal axis of the suspension; and a pseudo symmetry structure that is not a microactuator disposed on a second and opposite side of the central longitudinal axis and in generally mirror relation to the microactuator, the pseudo symmetry structure being generally symmetric about two horizontal axes and having a central hole formed therein, and having a mass that is within 20% of the mass of the microactuator and a stiffness that is within 40% of the stiffness of the microactuator in order to compensate for the mass and stiffness of the microactuator, thus making the suspension more mechanically symmetric about the longitudinal axis.
 2. The suspension of claim 1 wherein the pseudo symmetry structure has a mass that is equal to the mass of the microactuator to within 5%.
 3. The suspension of claim 1 wherein the pseudo symmetry structure has a stiffness that is equal to the stiffness of the microactuator to within 20%.
 4. The suspension of claim 1 wherein the pseudo symmetry structure has a stiffness that is equal to the stiffness of the microactuator to within 5%.
 5. The suspension of claim 1 wherein the pseudo symmetry structure has a mass and a stiffness that are equal to the mass and the stiffness of the microactuator, respectively, each to within 20%.
 6. The suspension of claim 1 wherein the pseudo symmetry structure comprises a spring formed integrally in a stainless steel component of the suspension, the spring having a stiffness that gives the pseudo symmetry structure a stiffness that generally balances a stiffness of the microactuator.
 7. The suspension of claim 1 wherein the pseudo symmetry structure is integrally formed with another component of the suspension.
 8. The suspension of claim 7 wherein the pseudo symmetry structure has a different thickness from said other component of the suspension with which it was integrally formed.
 9. The suspension of claim 7 wherein said other component of the suspension comprises at least one of a mount plate, a beam portion of a load beam, and a gimbal tongue.
 10. The suspension of claim 1 wherein the pseudo symmetry structure is formed separately and thereafter affixed to either a mount plate or a load beam of the suspension by at least one of an adhesive and welding.
 11. A suspension for a hard disk drive having: a microactuator on a first side of a central longitudinal axis of the suspension; and a pseudo symmetry structure that is not a microactuator disposed on a second and opposite side of the central longitudinal axis and in generally mirror relation to the microactuator, the pseudo symmetry structure having mechanical properties generally corresponding to the microactuator in order to compensate for the mechanical properties of the microactuator, thus making the suspension more mechanically symmetric about the longitudinal axis; wherein the pseudo symmetry structure comprises stainless steel and is integrally formed with the suspension, and the pseudo symmetry structure has a generally ring shape having a central hole therein.
 12. The suspension of claim 11 wherein the microactuator comprises a single non-split piezoelectric element and the second side of the suspension has no microactuator thereon and is in mass balance and inertial balance with the first side of the suspension to within 10%.
 13. The suspension of claim 12 wherein said mass balance is to within 5%.
 14. A method comprising actuating the microactuator on the suspension of claim
 11. 